Cathode ray tubes with electron beam deflection amplification



Feb. 17, 1970 J. DESCHAMPS 354565406 CTHODE RAY TUBES WITH ELECTRO BEAMDEFLECTION MPLIFICATION Original Filed Sept. 2. 1966 +J T.|l

i N v EN ro R.' n Jacque.: BESCIMMPS BY v ATroRNEY Int. ci. Ho1j29/70,29/74 U.S. Cl. 315-17 6 Claims ABSTRACT 0F THE DISCLOSURE The presentinvention provides a cathode ray tube having 'a quadrupolar lens foramplifying deflections of the electron beam, wherein a post accelerationdevice consisting of a dome-shaped electrode placed between thequadrupolar lens, which is utilized for amplifying deflections of theelectron beam, and the fluorescent screen so as to surround at least aportion of the lens. The domeshaped electrode is provided with a slotwhose center line coincides substantially with the locus of thecross-overs of the electrons that traverse the lens. The internal wallof the tube, extending from the uorescent screen to the dome-shapedelectrode, is coated with a conductive coating which is maintained,together with the fluorescent screen, at a high direct-current potentialwith respect to the dome-shaped electrode.

This is a continuation of U.S. application Ser. No. 577,050, filed Sept.2, 1966, now abandoned.

The present invention relates in general to cathode ray tubes of thetype in which the deection of the electron beam is amplified by electronlenses, and more particularly to a tube of this type having an improvedpost-acceleration device.

In known cathode ray tubes post-acceleration may be provided to increasethe energy of the electrons after the electron beam has been decctedboth horizontally and vertically, thereby obtaining on the fluorescentscreen an increased brilliance. However, the helical and grid inducedarrangements used at present for this purpose possess certaindisadvantages in that helical post-acceleration reduces the sensitivityof the tube, and post-acceleration with the aid of a grid, placed infront of the screen, causes a decrease in the resolution and contrast.

It is therefore a principal object of the present invenr tion to providean improved tube in which post-acceleration is achieved without theabove-mentioned disadvantages in a cathode ray tube having a quadrupolarelectron lens.

It is an object of the present invention to provide a post-accelerationdevice for a cathode ray tube having a quadrupolar electron lens, whichcombination avoids or altogether eliminates the disadvantages inherentin known combinations of a similar nature.

It is another object of the present invention to provide a cathode raytube of the type described having an irnproved post acceleration device.

It is a further object of the present invention to provide a cathode raytube of the type described which provides for post acceleration of theelectron beam by simple and economical means.

, Quadrupolar electron lenses are known for amplifying the deflection ofelectron beams produced by conventional beam forming arrangementspassing a beam through a known deflection system. These lenses have adivergent action in one plane and a convergent action in a second3,496,406 Patented Feb. 17, 1970 plane, perpendicular to the first one.In the second plane all the trajectories or paths of the electronsintersect in a common intersection point, called the cross-over.

The present invention consists in providing a cathode ray tube having aquadrupolar lens for amplifying deflection of the electron beam, whereina post acceleration device is provided which includes a dome-shapedelectrode placed between the quadrupolar lens and the fluorescent screenso as to surround at least a portion of the lens, the dome-shapedelectrode being provided with a slot whose center line coincidessubstantially with the locus of the cross-overs of the electrons thattraverse the lens when the tube is operating and the geometric center ofthe domeshaped electrode coinciding substantially with the center ofdeflection of the nearest deflection system, and wherein the internalwall of the tube, extending from the fluorescent screen to thedome-shaped electrode, is coated with a conductive coating, theconductive coating and the fluorescent screen being arranged to bemaintained at a high direct-current potential with respect to thedome-shaped electrode.

With this arrangement, the electrons traverse the aperture of thedome-shaped electrode and continue their trajectory, without changingtheir direction, toward the screen upon which they impinge with a greatenergy.

These and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription of the invention when taken with the accompanying drawingswhich illustrate one embodiment of the present invention, and wherein:

FIGURE 1 shows schematically and in section, one embodiment of thepresent invention;

FIGURE 2 shows a quadrupolar electron lens used in the tube of FIGURE l,and

FIGURE 3 is a front view of an electrode used in the tube of FIGURE l.

In carrying the invention into effect according to one convenient modeby way of example, FIGURE 1 shows a cathode ray tube which includes anevacuated envelope 1 composed, for example, of glass, and containing anemissive cathode 2, heated by a filament 3, a Wehnelt electrode 4,focussing and accelerating electrodes S, 6 and 7, vertical deflectionplates 8, a first quadrupolar electron lens 9, horizontal deilectionplates 10, a second quadrupolar electron lens 11, a dome-shapedelectrode 12 provided with a slot 13, and a fluorescent screen 14. Theinternal wall of the tube bears a conductive coating 15 made, forexample, of graphite and extending from the screen 14 to the level ofthe dome-shaped electrode 12.

The sizes of the dome-shaped electrode 12 and its posit1o n within thetube are such that its geometric center colncides substantially with thecenter of the horizontal deflection, that is the virtual intersectionpoint of the electlrm trajectories in the plane perpendicular to theplates A source of voltage, not shown, enables the filament 3 to beheated, while a direct-current potential source S1 enables thepotentials of the various electrodes of the tube to be maintained atsuitable values. The indicated values represent merely examples whichmay be considered as orders of magnitude.

The screen 14 of the tube and the conductive coating 15 are maintainedat a high potential, of the order of 10 to 20 kv., with respect toground by means of a source S2. The horizontal deiiection plates areconnected to a time base, not shown, while the voltages or signals to bevisualized on the screen are applied between the vertical plates 8.

FIGURE 2 shows the well known arrangement of an electron lens such asthose designated by 9 and 11 in FIG- URE l. It is an electrostatic lensformed by four semicylindrical or hyperbolic electrodes 21, 22, 23 and24.

3 The electrodes 21 and 23 are maintained at a potential -l-V, and theelectrodes 22 and 24 at a potential -V. Polarized in this manner, thelens produces a divergent action in the direction X-X and a convergentaction in the direction Y-Y. In the latter direction amplification isobtained by over-convergence.

For the voltages of the lenses 9 and 11 of FIGURE 1, the values of 100and 300 volts, respectively, are indicated as an example.

In the tube of FIGURE l the quadrupolar lens 11 is the amplifying lens,properly speaking, while the lens 9 serves to correct the astigmatismproduced by the main lens 11. Moreover, the position of lens 9 betweenthe two pairs of plates 8 and 10 makes it possible for lens 9 to amplifythe vertical deflection produced by the plates 8.

FIGURE 3 is an elevation of the dome-shaped electrode 12 with its slot13, seen in section in FIGURE 1. The slot 13 has been represented in therectangular form, but it may alternatively have an elliptical form, orthe like.

In operation, if the voltages applied to the quadrupolar lens 11 aresuitably chosen, all of the trajectories or paths of the electrons passthrough the slot 13. In the vicinity of the dome-shaped electrode 12 theequipotential surfaces are substantially hemispheres having vas a centerthe center of the spherical dome, except in the space adjacent to theslot 13 where the equipotential surfaces are curved inwardly and form athin convergent lens having its center at the level of the slot.

Under these conditions, the electrons emerge from the slot 13 withoutchanging their direction. In eflect, in the horizontal plane there is nochange of direction because all the trajectories of the electrons areperpendicular to the equipotential surfaces (hemispheres) and in thevertical plane all electrons traverse the thin convergent lens whichdoes not effectively change their direction. Consequently, onlyacceleration is produced due to the very high voltage of screen 14 andcoating 15, and thus the electrons impinge upon the screen with greatenergy. The spots produced on the fluorescent screen are therefore of agreat brilliance and enable transistory phenomena of very short durationto be made visible.

Post-acceleration achieved in this manner does not have the defectswhich are inherent in the prior art systems wherein post-acceleration isaccomplished by a helix or by a grid. Moreover, the arrangement inaccordance with this invention presents the advantage of leaving thesensitivity of the tube independent from the high voltage applied to thescreen.

While I have shown and described one embodiment in accordance with thepresent invention, it is understood that the same is not limited theretobut is susceptible of numerous changes and modifications as known to aperson skilled in the art. For example, the present invention is notlimited to the specific embodiment described herein but encompasses allmodifications, for example, its applications to other prior art cathoderay tubes, as known to a person skilled in the art. Consequently, I donot wish to be limited to the details shown and described herein, butintend to cover all such changes and modifications as are encompassed bythe scope of the appended claims.

I claim:

1, A cathode ray tube comprising an envelope having a fluorescentscreen, an electron gun for producing an electron beam directed towardsaid screen, a deflection system disposed along the path of said beamfor deflecting said beam in two orthogonal directions, a quadrupolarelectrostatic lens for amplifying the beam deflections, a dome-shapedelectrode placed between said quadrupolar lens and said fluorescentscreen so as to surround at least a portion of said electrostatic lens,a conductive coating on the internal wall of said envelope extendingfrom said screen to the region adjacent said dome-shaped electrode5 andmeans for maintaining said conductive coating and said screen at a highdirect-current potential with respect to said dome-shaped electrode,said dome-shaped electrode being provided with a slot whose median linecoincides substantially with the locus of the cross-overs of theelectrons that traverse said lens when the tube is operating, and thegeometric center of said dome-shaped electrode coinciding substantiallywith the center of deflection of the nearest deflection system.

2. A cathode ray tube as claimed in claim 1, wherein said direct-currentpotential is of the order of l() to 20` kv.

3. In a cathode ray tube having beam generating means for generating anelectron beam, beam deflecting means comprising a first and a secondpair of plates for deflecting said electron beam, and a quadrupolarelectrostatic lens means for amplifying said beam deflections,post-acceleration means for accelerating said beam subsequent todeilection thereot` comprising a first electrode of hemispherical shapehaving an aperture therein disposed in the path of said beam, a targetto which said beam is directed and a second electrode encompassing thepath of said beam beyond said first electrode to said target, saidsecond electrode and said target being maintained at a high directcurrent potential.

4. The combination defined in claim 3 wherein said aperture is in theform of an elongated slot having its long dimension in substantialcoincidence with the locus of points formed by the beam cross-oversresulting from said beam deflecting means.

5. The combination defined in claim 3 wherein the geometric center ofsaid first electrode is in substantial coincidence with the center ofdeflection of said beam deflecting means.

6. The combination defined in claim 3, wherein a second quadrupolarelectrostatic lens is disposed between said first and said second pairof plates.

References Cited UNITED STATES PATENTS 2,114,572 4/1938 Ressler 315-172,919,381 12/1959 Glaser 315-31 2,954,499 9/1960 `Gundert et al 313-78 X3,042,832 7/1962 Owren 315-14 X 3,136,918 6/1964 Watson 315-14 3,373,3103/1968 Worcester 313-78 X RODNEY D. BENNETT, IR., Primary ExaminerMALCOLM F. HUBLER, Assistant Examiner US. Cl. X.R. 313-78

